1. Field of the Invention
This invention relates to mixing apparatus and, more particularly, to mixers of the type having magnetically driven mixing elements.
2. Description of the Prior Art
In the analysis of samples comprising various mixtures of fluids such as blood, serum, reagents, and the like, it has been common practice to employ permanent magnet bars, discs, pellets, etc., which are inserted into a sample cell chamber containing the materials to be mixed and which are rotated by magnetic means outside of the sample chamber for mixing the materials therein. While magnetic mixers have been widely adopted, they have not proven entirely satisfactory in all applications and particularly in the mixing of fluids having different viscosities. In this regard, because of viscosity differences some serums, for example, will float while others will sink when added to various reagents to form fluid layers within the sample chamber. As a result, extremely thorough mixing action throughout the entire chamber volume is required for such materials. This is especially true when using small volume, narrow sample cells, generally of rectangular cross-section, which utilize small sample quantities. With small quantities, thorough mixing even into the upper corners of the cell remote from the magnetic mixing bar is essential. This degree of mixing action is difficult to achieve in prior magnetic mixers since the magnetic mixing elements thereof are generally rotated continuously which establishes uniform flow patterns in the sample chamber which do not thoroughly mix the sample in its entirety.